Measles is a highly contagious viral illness characterized by fever, malaise, rash, cough, coryza, and conjunctivitis [1]. There are no known measles virus reservoirs outside of humans [2]. The epidemiology and transmission of measles and its complications will be reviewed here. The clinical manifestations, diagnosis, prevention, and treatment are discussed separately. (See "Clinical manifestations and diagnosis of measles" and "Prevention and treatment of measles".)

EPIDEMIOLOGY

Measles infection — Measles occurs worldwide; control efforts have substantially altered the global distribution [3]. Measles incidence has decreased substantially in regions where vaccination has been instituted; measles in the developing world has been attributed to low vaccination rates [4].

In developed countries during the prevaccine era, more than 90 percent of children acquired measles by age 15 years [5-7]. Following implementation of routine childhood vaccination at age 12 to 15 months, the age of peak measles incidence during epidemics in the United States shifted to six months of age. This is approximately the time at which transplacentally acquired maternal antibodies are no longer present if the mother has vaccine-induced immunity [8-10].

Worldwide, measles is a significant cause of morbidity and mortality. Precise incidence estimates are difficult to obtain because of heterogeneous surveillance systems and probable underreporting [11]. In 2000, measles was estimated to cause approximately 31 to 39.9 million illnesses worldwide with an estimated 733,000 to 777,000 deaths, making it the fifth most common cause of death in children under five years of age [11-13].

The World Health Assembly adopted the World Health Organization (WHO)/United Nations International Children's Emergency Fund (UNICEF) Global Immunization Vision and Strategy, which included a goal of 90 percent reduction in global measles mortality between 2000 and 2010 [14,15]. The WHO identified 47 "priority countries" to focus measles mortality reduction efforts; these nations jointly account for approximately 98 percent of measles deaths. The strategy in these nations includes the following measures: (1) measles immunization with a goal of >90 percent national coverage and >80 percent per-district coverage with two doses of vaccine; (2) surveillance activities, including case investigation and laboratory testing in all suspected cases; and (3) clinical management of measles cases, including administration of vitamin A [12,16].

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